The field of art to which this invention pertains is powder coatings made from aqueous dispersions of epoxy resins or polyethers derived therefrom and to the process for making such powder coatings.
Various methods have been proposed for making finely divided resin compositions. For instance, in U.S. Pat. No. 3,422,049, it has been proposed that normally solid synthetic organic polymeric thermoplastic resins be subjected to vigorous agitation in the presence of water and a block copolymer of ethylene oxide and propylene oxide as a dispersing agent, at a temperature above the point of the resin, and at a pressure sufficient to maintain the water in the liquid state until a dispersion is produced with the polymer reduced to a finely divided particle form, after which the dispersion is cooled below the melting point of the resin. The resin particles are then recovered from the dispersing medium.
Processes similar to that proposed in U.S. Pat. No. 3,422,049 are disclosed in U.S. Pat. No. 3,586,654 and 3,674,736.
According to U.S. Pat. No. 2,945,020 finely divided polyethylene powders are prepared by agitating polyethylene in a solvent-nonsolvent mixture at a temperature below the melting point of the polyethylene for a time sufficient to form fine particles.
Another process for making finely divided polyethylene using a solvent-nonsolvent mixture is proposed in U.S. Pat. No. 3,244,687. In this process, the polyethylene is dissolved in a solvent-nonsolvent mixture wherein the nonsolvent has a higher boiling point than the solvent. The solvent is distilled off leaving the polyethylene dispersed in the nonsolvent.
In Canadian Pat. No. 970,494 pigmented polymer particles are prepared by emulsifying a film forming resin in a continuous phase above the melting point of the resin, adding pigment, cooling the emulsion below the melting point of the resin and recovering the solid pigmented resin particles.
Canadian Pat. No. 900,069 discloses a process for making dispersions of epoxy, polyamide and alpha-substituted styrene resins using monomeric anionic, nonionic and cationic surfactants as dispersing aids.